1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication system.
2. Description of the Related Art
Conventional communication systems typically include one or more end user devices that may form communication links with one or more stations or nodes that are connected to a communication network. For example, conventional wireless communication systems include one or more base stations, which may also be referred to as node-Bs, for providing wireless connectivity to one or more access terminals (ATs), which may also be referred to using terms such as mobile units, user equipment, subscriber equipment, and mobile subscriber stations. Exemplary access terminals include cellular telephones, personal data assistants, smart phones, text messaging devices, laptop computers, desktop computers, and the like. Access terminals may also refer to modems within one or more of these devices.
Access terminals may access the communication system or network using a dedicated link or port. For example, in a wireless communication system, a mobile access terminal can establish a dedicated traffic channel with a base station. The access terminal and the base station may then exchange data via the dedicated traffic channel. For another example, in a wired communication network, a terminal or computer can access the network via a dedicated port. The access terminal may also access the communication system using a common channel or medium that is available to all access terminals that may want to access the communication system. For example, in a wireless communication system, the access channel may be a random access channel and the access terminal may send a connection request message to a base station randomly over the random access channel. Other access terminals may also be sending connection request messages using the same channel at the same frequency. For another example, in a wired local area network, terminals connected to the cables or wires may communicate with one another or with a common control system over a common channel.
In a conventional communication system, access terminals initiate communication by transmitting a probe containing connection request message over an access channel. After a few message exchanges between the access terminal and the network, a dedicated traffic channel may then be set up in response to the connection request and the dedicated traffic channel may be used for subsequent data transmissions. For example, the radio spectrum of a wireless communication system is a scarce resource and so traffic channels are not typically allocated until a base station receives a probe, such as a connection request message, from an access terminal. Accordingly, when an access terminal is idle (e.g., the access terminal does not have an active traffic channel connection to a base station) and wants to establish a traffic channel to transmit data traffic, the access terminal sends connection request messages via the random access channel. Once the connection request messages are received successfully by the system, a dedicated traffic channel is established between the access terminal and the network and the access terminal starts sending the data traffic over the traffic channel. When the access terminal has finished sending data, the dedicated traffic channel may be torn down to conserve radio resources, which may be used by other access terminals.
An idle access terminal may also choose to send a short burst of data traffic over the random access channel. The access terminal may be able to transmit the short burst without going through the traffic channel setup procedure. Consequently, transmitting data over the access channel can potentially reduce the delay by avoiding the time for connection setup. Access channel transmission may be especially attractive for delay sensitive applications such as push-to-talk call setup messages. However, sending data over the access channel also has some drawbacks. For example, access channel collisions between concurrent data transmissions from multiple access terminals may cause some or all or the concurrent data transmissions to fail. For another example, transmission over access channels is usually less spectrally efficient than transmission over traffic channels, particularly in a wireless communication system. In a CDMA system, an access channel's transmission efficiency is worse than that of the traffic channel because of lack of closed loop power control and soft handoff. In general, the successful rate of data transmission over the access channel is smaller than the successful rate of data transmission over the traffic channel.
Conventional access terminals decide whether or not to use the access channel to transmit data based on the amount of data to be sent. For example, the access terminal may use a parameter, AccessPayloadMax, which indicates a threshold value for the size of the data block. For example, the parameter, AccessPayloadMax, may be set to 200 bytes. If the number of bytes in a data burst is less than the number of bytes indicated by the parameter, AccessPayloadMax, then the data burst can be transmitted over the access channel. However, if the number of bytes in a data burst is greater than the number of bytes indicated by the parameter, AccessPayloadMax, then the data burst must be transmitted over a traffic channel. Consequently, the access terminal may need to transmit a connection request message or probe over the access channel and a traffic channel may need to be set up to carry the data burst.